Doctors said the 90-minute procedure went "exceedingly well" at George Washington University Hospital.

Cheney walked out of the hospital Saturday afternoon waving to spectators and commenting that he felt good but had a sore shoulder.

The vice president plans to return to work Monday, and doctors did not recommend that he reduce his workload.

After the operation, Cheney took a call from President Bush, who told reporters at Camp David in Maryland that he does not expect the vice president to slow down.

"I know he ought to work at a pace he is comfortable with. And I know Dick Cheney well, and if I were to say, `You've got to slow down, Mr. Vice President,' he's going to say, `Forget it,' because he's got a job to do, and he's a valuable member of my administration,' " Bush said as he met with Japanese Prime Minister Junichiro Koizumi.

Cheney has a history of heart problems. He had his first of four heart attacks in 1978 at age 37. Cheney's health has raised questions about his ability to complete his term and the possibility of another Bush-Cheney ticket in 2004.

Although this is Cheney's third hospitalization since the November election, his doctors were careful to stress that the procedure was preventative and did not indicate that the vice president's condition was worsening.

"This device is going to be invisible to him," said Dr. Jonathan Reiner, director of the cardiac catheterization department at the hospital. "It really is an insurance policy."

The battery-operated device, known as an implantable cardioverter defibrillator or ICD, is more sophisticated than a standard pacemaker because it can slow down a fast heartbeat like a defibrillator or speed up a slow heartbeat like a pacemaker.

Cheney, 60, called the device a "pacemaker plus," and about 150,000 Americans have one.

Doctors recommended the procedure after a monitoring device he wore recorded four brief episodes of rapid heartbeat. Rapid heartbeats can be predictive of future life-threatening problems.

Cheney was sedated during the surgery, which involved doctors inserting the 3-ounce, pager-like device on the left side of his body just under his collarbone.

Doctors said the defibrillator portion of the pacemaker operates like an "internal cardiologist." It recognizes any abnormality that is life-threatening or would cause a loss of consciousness and corrects the problem within 10 seconds by sending an electrical pulse to either slow down the heart or speed it up. If a shock is needed, Cheney will feel a "pop," doctors said.

"It's much less dramatic than what's shown in the movies," Dr. Reiner said, referring to the electrically charged paddles that are applied to the outside of the chest in cardiac emergencies. "His hair will not stand on end."

Implanting the device reduces the vice president's risk of sudden death from an irregular heartbeat to less than 1 percent, but doctors said it will not reduce the risk of another heart attack.

Although Reiner said Cheney's prognosis was "terrific" and his life expectancy was "excellent," he acknowledged that the vice president has suffered a "moderate amount of damage" from his previous heart attacks.

Cell phones and strong magnets can disrupt pacemakers, but doctors played down any impact on Cheney's daily routine. He has been advised to use a cell phone only next to his right ear, farthest away from the device.

Cheney's heart condition has received considerable attention because of his broad influence in the Bush White House. He ran Bush's shortened transition period, oversees the administration's relationship with Congress and is in charge of the development of a national energy policy.

"Dick Cheney is playing the largest role of any of the vice presidents in American history," said Allan Lichtman, a presidential scholar and professor of history at American University. "Our government is far larger and far more complex. It's the natural evolution of the presidency to have the vice president take on more work."